The Berlin North-South main line (German: Nord-Süd-Fernbahn), also called the North-South link (Nord-Süd-Verbindung) is an electrified railway line in Berlin which was opened in 2006. It is an important component of the “mushroom concept” (Pilzkonzept) adopted for long-distance and regional rail services through the city. Its core is an approximately long Tiergarten tunnel under the Tiergarten in Berlin. The tunnel section includes the underground level of Berlin Hauptbahnhof (main station) and the Potsdamer Platz regional station. The above-ground section of the line includes the Berlin Südkreuz station. Route General The line is a four-track connection between the Ringbahn (Ring line) in the north of Berlin via the Berlin Hauptbahnhof to Südkreuz and the Anhalt Railway in the south. North of the Hauptbahnhof the line divides into two double-track lines. One of them runs east, the other west, both running on to the Ring line. The tunnel and the connection to the northeast are entirely new lines. The connection from the tunnel to the north-west to Moabit follows the course of the Lehrter railway. The southern section runs above ground through the former yards of the Anhalt Railway. Northern section The route from Wedding junction starts at a grade-separated junction towards the southwest from the Ring line’s mainline tracks. It first crosses over the southern mainline track of the Ring line, and is rising. It then runs across a bridge, called the Überflieger (overflyer) that crosses the Berlin-Spandau navigation canal, Perleberger Straße (street), the lines of the old Lehrter railway, the freight lines serving the Hamburger and Lehrter stations and one of the tracks of the new Lehrter line. The line descends to the south and reaches the level of the tracks of the Lehrter railway at the entrance to the tunnel and then descends a ramp with a gradient of 2.5 per cent. Tunnel Not far beyond the tunnel entrance is the lower level of the Berlin Hauptbahnhof with its eight platforms. South of the station the line passes under the Spree river. The tunnel turns southeast to Potsdamer Platz station and then back to the south. It passes under the Landwehr Canal and rises to the surface again near of Gleisdreieck U-Bahn station on a ramp with a gradient of 3.0 per cent. Southern section East of the tunnel exit is the site of the disused Anhalter freight yard. The bridges on the line over Yorckstraße lie between the